Process for melt spinning polyethylene terephthalate



1963 E. WESTERHUIS ETAL 3, 0 7

PROCESS FOR MELT SPINNING POLYETHYLENE TEREPHTHALATE Filed June 21, 1960 f'1g l 119-2. l0

EGGO WESTERHU l S KAREL H. KOK

INVENTORS.

ATTORNEY United States Patent 3,100,675 PROCESS FUR MELT SPlNNiNG POLYETHYLENE TEREPHTHALATE Eggo Westerhuis, Arnhem, and Karel Herman Kok,

Dcesburg, Netherlands, assignors, by mesne assignments, to N. V. ()nderzoekingsinstituut Research, ikrrxilgem, Netherlands, a corporation of the Nether- Filed June 21, 196i), Ser. No. 37,714 Claims priority, application Netherlands July 28, 1959 3 Claims. (Cl. 18-54) This invention relates generally to a process for the manufacture of polyethylene terephthalate filamentary material and more particularly to a process for melt spinning polyethylene terephthalate filamentary material.

It has been proposed that polyethylene terephthalate filamentary material be produced by extruding molten polyethylene terephthalate through a spinneret into a gaseous cooling medium to cool and solidify the filaments. Thereafter, the filaments are collected in package form, unwound, stretched, and taken up in a twisted or untwisted state. This process does not produce a yarn of substantially uniform denier with the result that articles manufactured from such yarn do not have a uniform appearance. In addition, stockings knitted from such yarns exhibit to a substantial degree a barre effect which is, of course, undesirable.

It is, therefore, an object of the present invention to provide an improved process for the melt spinning of polyethylene terephthalate.

It is a further object of this invention to provide a process for the melt spinning of polyethylene terephthalate that is free of the ditficulties of the prior art.

A further object of this invention is to provide a process for the melt spinning of substantially uniform denier polyethylene terephthalate.

Another object of this invention is to provide a process for the melt spinning of polyethylene terephthalate filamentary material which material when used in a fabric produces one of uniform appearance.

These and other objects will become apparent to one skilled in the art from a reading of the following detailed description taken in conjunction with the drawing in which:

FIGURE 1 is a side elevational view of the melt spinning apparatus of this invention;

FIGURE 2 is a front elevational view, partly in section,

I of the apparatus of FIGURE 1;

FIGURE 3 is an enlarged perspective view of the insulator per se;

FIGURE 4 is a bottom view of a spinning plate according to this invention; and

FIGURE 5 is a bottom'view of another spinning plate according to this invention.

It has now been found that if the melt spinning of polyethylene terephthalate is conducted in a certain prescribed manner, the yarn so produced will be of a substantially even denier and when formed into a fabric, the fabric will have a uniform appearance.

It is essential to the successful operation of this invention that the molten polyethylene terephthalate he extruded at a temperature of at least 268 C. through a spinning plate containing a plurality of orifices. This plate must be maintained at a temperature of at least 268 C. and the orifices in the plate must be the same distance apart and the distance between adjacent rows must be less than the distance between orifices in a row. The freshly extruded filaments must be insulated from the ambient atmosphere for a distnace of 7 to 14 centimeters immediately after they leave the spinning plate. Thereafter a gaseous cooling medium is directly transversely across the filaments at a velocity of at least 25 centimeters per second and in a bient atmosphere.

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direction parallel to the rows of orifices. The filaments are thus cooled and solidified and are thereafter collected in a conventional manner.

The threads resulting from the above process possess a substantial uniformity of denier. This means that the difference between the largest and smallest thread diameter is substantially less than that heretofore attainable. The same is usually determined per 200 meters of thread and is expressed in percentages of average thread diameter.

The polyethylene terephthalate in molten form may be obtained by any conventional means. For example, it is possible to use grids or extruders to obtain the molten polymer. It is only essential that the polymer melt have a temperature of at least 268 C. just before extrusion through the orifices of the spinning plate or spinneret. Higher temperatures, of course, may be used; however, the same should not be so high as to degrade the polymer.

The temperature of the spinning plate or spinneret through which the molten polymer is extruded must also be maintained at a temperature of at least 268 C. This temperature is determined at the outer surface of the spinning plate. Higher temperatures may be used for still further improvements in the resulting threads. The number of flues and fibers which project from the threads and cause difficulties in weaving are substantially reduced. In addition, the dye affinity and elongation'of the threads are increased. Normally, the temperature of the melt will be slightly higher than the temperature of the spinning plate.

The orifices in the spinning plate or spinneret may be arranged in several ways. It is only essential that the orifices be arranged in parallel rows, that the orifices in a given row be equally spaced, and that the distance between adjacent rows be less than the distance between the orifices in each row. It is preferred that the distance between successive rows be equal and that the distance between adjacent orifices be greater than 5.5 mm.

It is also preferred that the distance between the first and last orifices in a row and the rim of the spinning plate be as large as possible. This distance, of course, depends upon the size of the spinning plate, and the diameter and number of orifices. It is thus possible to arrange the orifices in staggered relationship to each other and also to arrange them in parallel relationship.

The insulated space immediately adjacent the face of the spinning plate completely encircles the spinning plate and insulates the freshly extruded filaments from the am- The same must not be less than 7 centimeters nor more than 14 centimeters in length. If the same is too short, the cooling gaseous medium will cool the spinning plate to below its critical temperature, thereby requiring greater control of the same and thus increasing the cost of the operation. If the same is too long, the cooling and solidification of the filaments is delayed with the result that the uniformity of denier is reduced.

The gaseous cooling medium which cools and solidifies the filaments must have a velocity of not less than 25 centimeters per second or the uniformity of the filaments will be reduced. The gaseous medium is normally cool air and the same contacts the filaments in a conventional blow box. In order to reduce turbulence, the back wall of the blow box through which the air blows is permeable and may be composed of one or more sieve plates, layers, of gauze, or fabrics.

It is preferred that the speed of the gaseous cooling medium be atleast 30 centimeters per second because greater uniformity is obtained at these speeds. The speed should not be so great as to cause sticking of the filaments, which maximum speed is easily determined by those skilled in the art taking into consideration the number and denier of the filaments.

The length of the blow box or the distance through should meet certain requirements.

which the filaments are contacted with the gaseous cooling medium is preferably 75 to 100 centimeters. The most favorable results are obtained if such is used.

Elimination of any one of the foregoing critical conditions will resuult in a reduction of the uniformity of the resulting yarn denier. Thus, it is necessary if the most uniform denier yarn is to be obtained that each of these conditions be met.

In order that this invention may be more fully understood, one embodiment thereof will now be described by way of example with reference to the accompanying drawing.

Referring to FIGURES 11 and 2, reference numeral denotes a spinneret assembly from which the molten polyethylene terephthalate is extruded in a known manner through orifices in the spinning plate 11. The blow box assembly is indicated generally by numeral 12 and is composed of compartments 13 and 14. A curved side wall 15 integrally forms three sides of compartment 13 and interconnects side walls 16 and 17 of compartment 14. The walls are flanged and hermetically sealed together by conventional securing means, such as bolts and nuts 18 disposed on'opposite sides of the assembly 12. Compartments 13 and 14 are separated by a thin air permeable filter 19 which is fastened therebetween in the blow box assembly 12.

Air is supplied to compartment 13 from the bottom thereof. The air is under slight pressure in order that it may have the required velocity of at least 25 centimeters per second as it is directed transversely across the filaments in compartment 14. Filter 19 diffuses the air as it enters compartment 14 and thereby reduces turbulence. The air cools the yarn formed during the spinning operation and carries any vaporous materials out of compartment 14 into the atmosphere.

Blow box 12 is spaced from the spinneret assembly 10 by aninsulating member 20 as is more fully shown in FIGURE 3. Insulating member 211 is square or rectangular shaped depending upon the shape of the upper end of, the blow box 12. That is, it should correspond approximately in width and depth to that of the top of the blow box. The height of insulating member 20 should not be less than about 7 centimeters and not more than about 14 centimeters. As indicated above, the freshly spun filaments must be insulated from the ambient atmosthe height of member 20 is controlled by this distance and depends upon how far into the same the spinning plate 11 extends.

The insulating member 21} is attached to blow box'assembly 12 by conventional securing means, such 'as nuts and bolts 21 to form a rigid self-sustaining structure. The assembly 12 together with insulating member 20 is urged against the bottom of spinneret assembly 10 to form a substantially air tight association therebetween. In the alternative, member 20 may, of course, be attached to the spinneret assembly 10. Further, member 2% may be hinged in the back, for example, in order that it may be opened in the front for better access to the spinneret assembly.

Member 20' may be of one piece construction as illustrated in FIGURE 3 or it may be constructed of several parts either in the circumferential direction or in the direction of the filament movement. Thus, one or more of the parts of the member may be removed for easy access to the spinneret assembly 10.

The type of material used in insulating member 20 First, the material must have good non-heat conducting or heat insulating properties; second, it must withstand the high temperature of the spinning environment; and third, the material should not be made from substances that tend to flake off or break in use.

Materials having good non-heat conduction properties 'as referred to above are these substances which have relatively low heat conductive factors. For example, member 20 having a heat conductivity of about 0.01 or less is satisfactory. Heat conductivity is the heat in calories which is transmitted per second through a plate one centimeter thick across an area of one square centimeter when the temperature difference is one degree centigrade.

Suitable materials for use in the present invention are asbestos cement products, Marinite, Transite and Formica. Any other known material meeting the aforesaid requirements may be used.

The insulating member should have a wall thickness that is sufficient to give good insulating properties. For example, a wall thickness of 5 centimeters has been found to be effective for an asbestos cement product. Greater wall thickness, however, may also be used, if desired.

The blow box assembly 12 is made of metal, usually aluminum. However, other metals may be used if desired. The spinneret assembly is composed of stainless steel or other comparable material suitable for use in the spinning environment.

Referring now to FIGURES 4 and 5, reference numeral 22 denotes the spinning orifices in spinning plate 11 through which molten polyethylene terephthalate is extruded. Orifices 22 are conventional spinning orifices and may consist of a wide cylindrical portion, a conically tapered portion and a narrow cylindrical portion.

Orifices 22 are arranged in rows parallel to each other and in a straight line in eachrow. The distances between orifices 22 are equal in all rows and usually at least 5.5 mm. The orifices 22 may be arranged opposite or in staggered relationship to each other.

The distance between successive rows of orifices are equal but less than the distance between adjacent orifices in a row. The gaseous cooling medium flowing from compartment 13 through compartment 14 flows parallel to e rows of orifices as is more clearly shown by the arrow in FIGURE 4.

To further illustrate this invention, the following examples are presented. It should be understood that the same are offered merely for the purpose of illustration Granular polyethylene terephthalate having a specific viscosity of 0.60 and a moisture content of less than 0.01% by weight was melted on a conventional grid heated by a gaseous medium at 284 C. Themolten polymer at a temperature of 275 C. was forced through orifices 22.0f the spinning plate 11 of FIGURE 4. The orifices 22 had a diameter of 250 microns and were spaced7 mm. apart in each row, which rows were 5 mm. apart.

During the spinning, the lower surface of spinning plate 11 had a temperature of 271 C. Immediately below plate 11 and adjacent thereto was arranged insulating member 20 constructed of an asbestos cement product, Syndanio (marketed by Turner Asbestos Cement Company). The height of member 20 was 12 centimeters. Positioned below and secured to member 20 was a blow box assembly 12. Air. at room temperature was passed through compartment 13 and filter 19 composed of gauze. The air moved in compartment 14 transversely to the molten filaments falling downwardly through the same, and flowed parallel to the rows of orifices 22. The velocity of. the air was 45 centimeters per second and the zone through which the filaments'were exposed to the air was 75 centimeters in length. The quantity of the air was 1400 liters per minute.

The resulting threads were wound and subsequently stretched to a denier of 50.4 and a filament denier of 1.8. The denier evenness was 2.5%.

Additional polymer was spun in an identical manner except the orifices 22 were arranged in an equilateral triangular pattern, one side o-f which was 4.5 mm. in length.

The resultant threads had a denier evenness of 4.7%.

Also, under identical conditions, except with insulating member 20 having a height of 15 centimeters, the resulting thread had an evenness of 4.1%.

Example II Polyethylene terephthalate similar to that :of Example I was spun in the same manner as that of Example I except the molten polymer had a temperature of 281 C., and a pair of spinning plates 11 of the type shown in FIGURE 5 were fixed in the same spinning assembly 10, and maintained at 271 C. The distance between orifice was mm. and the distance between rows was 6 mm.

The insulating member 20 had a height of 13 centimeters, the air had a velocity of 44 centimeters and the volume of air was 2000 liters per minute. All 'other operating conditions and operations were the same as in Example I.

The resulting thread had a denier of 100, a filament denier of 2.7, and a denier evenness of 2.5%

The foregoing demonstrates that by carefully following the conditions specified herein, one is able to obtain polyethylene terephthalate threads of substantially uniform denier.

It should be understood that various modifications may he made in the invention without departing from its spirit and scope which is to be limited only by the following claims.

What is claimed is:

1. A process for the production of polyethylene terephthalate filamentary material comprising the steps of extruding molten solvent free polyethylene terephthalate at a temperature of at least 268 C. through a spinning plate containing a plurality of orifices, said spinning plate Ibeing maintained at a temperature of at least 268 C., forming said molten polyethylene terephthalate into a plurality of filaments, arranging said filaments in a plurality of parallel rows wherein the distances between orifices in one row are about 5.5 to 10 mm., said filaments within each now being equally spaced, said rows being so spaced that the distance between each row is less than the distance between said equally spaced filaments, insulating said filaments from the ambient atmosphere for a distance of from 7 to 14 centimeters and thereafter passing a cooling gaseous medium transversely across \said filaments, said medium having a velocity of at least 25 centimeters per second and being directed parallel to said plurality of parallel rows of filaments.

2. A process according to claim 1 wherein said gaseous medium has a velocity of at least 30 centimeters per second.

3. A process according to claim 1 wherein said filaments are exposed to said gaseous medium for a distance of to centimeters.

References Cited in the file of this patent UNITED STATES PATENTS 2,252,684 Bahcock Aug. 19, 1941 2,273,105 Heckert Feb. 17, 1942 2,804,645 Wilfong Sept. 3, 1957 2,924,503 Reese Feb. 9, 1960 FOREIGN PATENTS 546,723 Canada Sept. 24, 1957 

1. A PROCESS FOR THE PRODUCTION OF POLYETHYLENE TEREPHTHALATE FILAMENTARY MATERIAL COMPRISING THE STEPS OF EXTRUDING MOLTEEN SOLVENT FREE POLYETHYLENE TEREPHALATE AT A TEMPERATURE OF AT LEASR 168* C. TTHROUGH A SPINNING PLATE CONTAINING A PLURALITY OF ORIFICES, SAID SPINNING PLATE BEING MAINTAINED AT A TEMPERATURE OF AT LEAST 268* C., FORMING SAID MOLTEN POLYETHYLENE TEREPHTHALATE INTO A PLURALITY OF FILAMENTS, ARRANGING SAID FILAMENTS IN A PLURALITY OF PARALLEL ROWS WHEREIN THE DISTANCES BETWEEN ORIFFICES IN ONE ROW ARE ABOUT 5.5 TO 10 MM., SAID FILAMENTS WITHHIN EACH ROW BEING EQUALLY SPACED, SAID ROWS BEING SO SPACED THAT THE DISTANCE BETWEEN EACH ROW IS LESS THAN THE DISTANCE BETWEEN SAID EQUALLY SPACED FILAMENTS, INSULATION SAID FILAMENTS FROM THE AMBIENT ATMOSPHERE FOR A DISTANCE OFF FROM 7 TO 14 CENTIMETERS AND THEREAFTER PASSING COOLING GASEOUS MEDIUM TRANS VERSELY ACROSS SAID FILAMENTS, SAID MEDIUM HAVING A VELOCITY OF AT LEAST 25 CENTEMETERS PER SECOND AND BEING DIRECTED PARALLEL TO SAID PLURALITY OF PARALLEL OF FILAMENTS. 